Hydraulic apparatus



Dec. 8, 1953 c, E A M 2,661,766

HYDRAULIC APPARATUS riginal Filed March 12, 1947 2 Sheets-Sheet l b X Fl6. 4

109 INVENTOR.

CECIL E. ADAMS BY cum Dec. 8, 1953 c. E. ADAMS 2,661,766

HYDRAULIC APPARATUS Original Filed March 12, 194'? 2 Sheets-Sheet 2 3 INV EN TOR.

5 CECIL E. ADAMS BY 7% KMW Pat ented Dec. 8, 1953 2,661,766 HYDRAULICAPPARATUS Cecil E. Adams, Columbus, Ohio, as'signor to The I DenisonEngineering Company, Ohio, a corporation of Ohio Columbus,

,originalapplication March 12, 1947, Serial No,

743,127, now Patent No. 2,569,213, datedv Sep- 'tember 25, 1951. Dividedand this application June 15, 1948, Serial N 33,211

1 a This application is a division of my copending application, SerialNo. 734,127, filed March 12, 1947 for Hydraulic Motor Control Apparatusnow Patent No. 2,569,213, dated September 1951. 6

- This invention relates generally to the science or hydraulics and isparticularly directed to a hydraulic circuit and hydraulic apparatuscontained within the hydraulic circuit.

One of the objects of the invention is to provide a hydraulic circuitfor hydraulic apparatus of the type having a movable element, thecircuit including means for causing delayed action of the movableelementin the apparatus.

Another object of the invention is to provide a time-delay valve for usein a hydraulic circuit containing a power cylinder, the latter having apiston for reciprocatory movement in the cylinder, the time-delay'valvebeing-operative to cause the piston to remain in a certain position fora predetermined period of time before completing a desired cycle ofmovement.

Another object of the invention is to provide a time-delay mechanism foruse in a hydraulic circuit, the time-delay mechanism being operatedprincipally by hydrostatic pressure.

A still further object of the invention is to provide a time-delaymechanism of the type mentioned in the preceding paragraphs with meansfor varying the length of the delay caused by such mechanism. a

Another object of the invention is to provide a hydraulic circuit with atime-delay mechahism which is fully automatic in operation, thuseliminating any additional requirements for action on the part of theoperator of the mechanism in which the hydraulic circuit isincorporated.

' Still another object of the invention is to provide a hydrauliccircuit including a source of fluid pressure and a power unit withacontrol mechanism including a fluid pressure responsive valve which isoperative to efiect automatic forward and reverse action of the powerunit and providing the circuit with a time-delay mechanism for causingthe power unit to be retarded in its transition from forward to reverseoperation.

Another object is to provide a time-delay mechanism of the typementioned in the preceding paragraph which is set for operation by apressure drop in the system and becomes operative when the pressure'dropis diminished.

Still another object of the invention is to p v de a time-delaymechanism for use in a r .6 Claims. (01. 137-689) hydraulic circuit,themechani'sm having a spool valvebiased by a spring toward a closedposition and opened in opposition t'othe spring by fluid pressure whencertain'action takes place in the hydraulic system, the spool valvebeingclosed by the spring when the above-mentioned condition changes, themovement of the spool valve to the closed position being retarded by aslow dissipation of fluid from the space in front of the spool valve} Anobject of the invention also is to provide a hydraulic press having ahydraulic circuit including a source of fluid pressure, a powercylinder'for operating the'ram of the press, a valve mechanism forcontrolling the operation of the power cylinder,this mechanism having anautomaticreversing valve moved in one direction by fluid pressure, and atime delay mechanism for applying fluid pressure to the reversing valveto' maintain the same in a position to direct fluid pressure from thesource to a certain portion of the power unit; the'time-delay mechanismincludes a spool valve which is biasedtoward a closed position by aspring and toward an open position in opposition to'the spring by apressure differential existing when fluid "is directed from the pressuresource to the power cylinder to cause movement of the ram in onedirection, the spring serving to return the spool valve to a closedposition when the pressure differential is diminished by theinterruption of ram movement, the time-delay mechanism including anorifice through which fluid is displaced by the spool in moving toward aclosed position, the resistance-caused i by the orifice retarding themovement ot the spool to delay the closing of the valve, 'this' delay''serving to lengthen the period of time fluid pressure is applied to thereversing valve and consequently the time period during which the ramexerts pressure on the work prior to making a return stroke.

An object also is to provide a time-delay mechanism of the typementioned in the preceding paragraph with a fixed orifice and means forchanging the potential travel of the spool to vary the length of thedelay caused by the mech- It'is an' object of the invention to provide ahydraulic circuit for a hydraulic mechanism of the typehaving a cylinderwith a reciprocatory piston anda control mechanism for governingtheoperation of thepiston, the control mechanism having-a reversingvalve which is main tained in aposition to cause movement of thepiston'ina selected direction through the utilization of fluiddischarged from the cylinder while the piston is moving in suchdirection, the cessation of fluid discharge, due to the interruption ofmovement of the piston, permitting the reversing valve to shift to aposition to cause reverse movement or the piston, the circuit beingprovided with a mechanism for delaying the shifting of the reversingvalve for a predetermined time after the piston stops moving, thetime-delay mechanism being automatically set for operation when thepiston moves in theselected direction and released for operation whenthe piston stops moving in such direction.

Another object is to provide a time-delay mechanism for a hydrauliccircuit; which mechanism is provided with a flow resisting elementconsisting of a group of reduced orifices spaced in a series whereby theeffect of a single minute orifice may be secured without the danger ofstoppage attendant thereto, the use of a group of larger orifices alsopermittingthe employment. of substantial material and still maintain:the ratio of diameter to length of orifice. most conducive to aminimization of the effect of changes in viscosity of the hydraulicfluid due to temperature variations.

Further obj ects and advantages of the present invention will beapparent from the following description, reference being had to'theaccom panying drawings wherein a preferred form of embodiment of theinvention is clearly shown.

In the drawings:

a Fig. 1 is a plan view of the time-delay valve formed in accordancewith the present invention.

Fig. 2 is a detail horizontal sectional view taken through the valveshown in Fig. 1.

Fig. 3 is a detail "sectional view taken through a portion of the valveon the plane indicated by the .line III-III of Fig. 2.

Fig. 4 is a similar view on an enlarged scale taken through a portion ofthe valve on the plane indicated by the line IV--IV of Fig. 3.

Fig. 5 is a diagrammatic view of a hydraulic system for a hydraulicpower cylinder, the time delay mechanism shown in Figs. 1 to 4 beingincorporated therein.

Referring more particularly to the drawings and especially to Fig. 5thereof, the numeral designates a hydraulic system in which thetimedelay valve, indicated generally by the numeral 2 l is connected.The circuit 20 includes a source of fluid pressure 22 having a fluidreservoir 23, a motor-driven pump 24 and a relief valve 25 for limitingthe pressure generated by the pump 24.

The circuit also includes a power cylinder 2'5 and a control valvemechanism 21 for governing the movement of a piston 28 contained withinthe power cylinder. The mechanism 21 may be of any suitable type, thatillustrated corresponding to a control valve mechanism'forming thesubject matter of my copending application Serial No. 589,163, filedApril 19, 1945, now Patent No. 2,491,355, issued December 13, 1949. Thisvalve mechanism includes a body 30 having -a bore 3! and a plurality ofannular grooves 32 to 31, in-

clusive, spaced longitudinally of the bore 3 I; This bore 31 receivesfor sliding movement a sleeve member 38 which is provided with aplurality of sets, 40 to 41' inclusive, of-latera-lly extending portswhich sets of ports are spaced longitudinally of the sleeve, these portsregistering in certain positions of movement of the sleeve, with certainof the grooves 32 to 31. The sleeve receives .a shuttle valve spool 48which is provided with an external groove 53 for connecting certainsetsof-pv sn different positions of longitudinal movement in the sleeve.This spool is biased toward the lower end of the sleeve by a coil spring5| disposed between the spool and a cap 52 secured to the upper end ofthe sleeve. I

A shipper rod 53 projects from the lower end of the sleeve 38 through acover 54 which is secured to the bottom of the body 30. This shipper rodreceives a collar 55 for engagement by an arm 56 which is carried by aram 51 projecting from the under side of piston 28. When the arm 56engages collar 55 movement will be transmitted to the shipper rod 53 andsleeve 38; this movement takes place only when the piston 28 is movingin an upward direction adjacent the termination of its upward stroke.Normally, the

sleeve 38 is held in a centered position by a coil spring 58 surroundingthe shipper rod and engaging a washer 60 at its upper end and a stopcollar til at its lower end. The washer Bil is arranged to engage ashoulder 62 which surrounds the lower end of bore 3 I, this shoulderserving to limit the upward movement of the washer. Collar 5.! engagesthe bottom wall of a counterbored hole through which the shipper rod 53projects; this arrangement permits movement of the sleeve in eitherdirection in opposition to the force of the spring 58. When the sleeve38 is moved upwardly by the final stage of upward movement of the piston28, ports 44 will be in registration with groove 34 so that fluidflowing from the pressure source to groove 35 will be conducted throughthe interior of the sleeve 38 and ports 44 to groove 34 I from which itmay flow through a second bore ing from the pressure source into 63 to agroove 64 which communicates with groove 36 and from groove 36 throughports 46, the interior of the sleeve 38 above spool 48 and outwardlytherefrom through ports 41 to groove 31 from which the fluid will flowthrough the upper end of bore 63 and through conduit 65 to reservoir 23.When the fluid follows this path pump 24 will operate under no load.

The body 30 is also provided with an annular groove 66 in communicationwith bore 63 below the point of communication of such bore with groove34. Groove 66 communicates with groove 32 as at 61, communicationbetween bore 63 and groove 32 over this path being normally precluded bya land 68 formed on a spool I0 disposed for longitudinal adjustment inbore '63. Spool 10 has an external groove H above land 68, this groovenormally providing for fluid flow from groove 34 to groove 64. When itis desired to initiate an operation of the power cylinder, spool 10 islowered through the actuation of a crank pin I2 until a land 13, at theupper end of spool 10 blocks groove 64, at which time groove II willestablish communication between groove 34 and groove 66. With spool Itso positioned fluid flowgroove 35 will pass through ports 45 to theinterior of the sleeve 38 and outwardly therefrom through .ports 44 togroove 34; this fluid then flows into bore 63 and downwardly to groove65 from which it will flow to groove 32.

r The fluid enters the sleeve 38 through ports 40 and exerts an upwardforce on the shuttle valve spool 48. This force moves the shuttle valvein opposition to the spring 5| to cause groove 50 to establishcommunication between ports 45- and 46. At this time fluid introduced togroove 35 from the source of fluidpressure will flow through ports 45 tothe interior of the sleeve 38 and out:- wardly therefrom through ports46 to groove 36. This fluid will then flow through passage I4 to theacumen upper end of power cylinder 28; the force of this fluid willactupon piston 28 to'urge it in a downward direction. This movement of, thepiston discharges fluid from the lower end of the power cylinder throughline to groove 33. Such fluid will then flow through ports 42'into atransverse passage 18 formed in the shuttle valve spool 48. From thispassage fluid will be discharged through an axial passage 11 in theshuttle valve and an extension 18 thereof in cap 52 to the groove 31from which it will flow to the reservoir 23. Due to the restriction ofport 11 a back pressure will lie-built up in passage 16, port 42, groove33, and line 15} as well as in the bottom portion of power cylinder 28.This back pressure will be. transmitted through a reduced passage 80 inthe lower portion of the shuttle valve to the lowerend of the chamber insleeve 38 beneath the shuttle valve, this pressure tending to retain theshuttle valvetin an elevated position during downward movement of thepiston 28.

Under normal conditions the back pressure will fall when piston 28ceases to-move in a downward direction for any reason, and when thisoccurs spring. 5| will return the shuttle valve to a lowered position inwhich fluid pressure from the pump 24 will be directed to the under sideof the piston 28 while the upper end of the power cylinder will be incommunication with the reservoir 23. At this time the force of the fluidwill move the iston 28 and ram 51 in' an upward direction in the returnstroke of the ram. When the ram and piston approach the upper limit ofthis return stroke, arm 56 will engage collar 55 on the shipper rod 53and move spool 38 upwardly until ports 44 again register with groove 34at which time fluid pressure from the source will be directed to thereservoir 23. It will be understood at this time that in the initialportion of the downward stroke of piston 28 arm 58 moves away fromcollar 55 permitting spring 58 to return'sleeve 38 'to its normalposition in which ports '44 are not in registration with groove 34.After this initial movement spool 18 may be returned to its normalposition either through the manual actuation of crank pin 12 orautomatically under the influence of spring 8I disposed between lowerend of the spool 18 and the bottom cover 54. 7

As set forth in the above-mentioned copending application crank pin 12may be employed to set spool 18 for the automatic operation of the powercylinder; that is, spool 18 will be retained in its lowered position inwhich groove 1I therein continuously establishes communication betweengroove 34 and groove 88. When spool 18 is so disposed the final stage ofupward movement of piston 28 will cause the registration of ports 44with groove 34 and fluid from the source of pressure may then flowdirectly to groove 32 to initiate another cycle of operation of thepower cylinder. The mechanism and operation thus far described areidentical with those of the copending application mentioned, theforegoing description having been given merely to facilitate theunderstanding of the present invention.

On some occasions in the use of the press mechanism above described, itis desirable in the operation of ram 51, to cause this ram to hesitateor dwell at the lower end of the downward or power stroke before thereturn stroke is initiated. One such occasion is found in the formationof belts for sanding machines wherein the ends of the belts arecoated'with adhesive and" pressed together with the press ram, theoverlapped ends communication between being squeezed together 6: apredetermined time period to permit the adhesive to set. Anotheroccasion is in the formation of die cast or certain plastic materialswherein the material is sub- 'jected to ram pressure while being heatedor while in a fluid or plastic state. To effect this hesitation or dwellof the. ram, a time-delay mechanism indicated by the numeral 2 I, hasbeen disposed in the hydraulic circuit. This time-delay mechanism is soconstructed and connected in the system that its operation will beaccomplished hydraulically and fully automatically. The timedelaymechanism 2| includes a bore 82 in a body 83, which body is providedwith a pair of ports 84 and 85 spaced longitudinally of the bore 82.Port 85 is connected by line 85 with groove 38 in body '38; port 84 isconnected by line 81 with groove 32. Bore 82 slidably receivesa spool 88in which an annular groove 98 is provided, this spool also having a wideland 9| at one end which normally obstructs communication between ports84 and 85. A narrower land 92 adjacent the opposite end of the spoolprevents communication between the groove 98 and the end 89 of bore 82adjacent the corresponding end of the spool. This end of bore 82 isconnected by-a line 93 with line 86, line '93 having a check valve 94disposed therein; this check valve permits unrestricted fluid flow fromline 86 into the end 88 of bore 82 and prevents fluid flow outwardlythrough line 93. A second line 95 also extends from this end of the bore82 to line 86, line 95 having flow-restricting means 96 disposedtherein; the purpose of this flowrestricting means will be set forthhereinafter.

The spool 88 is normally advanced toward a position to blockcommunication between ports '84 and 85 by a coil spring 91disposedbetween the end of a socket in the spool and a shoulder 98 on astop screw I88, threadedly received in a cap ID! for body 83. Stop screwI88 has an exteriorly disposed knob I82 by means of which this screw isadjusted in or out to regulate the degree of movement of spool 88. Inthe innermost position thereof stop screw I88 retains spool 88 inposition to prevent communication between ports 84 and 85 and rendersthe time-delay mechanism ineffective. By adjusting the screw outwardly adistance sufiicient to permit spool 88 to move far enough so that groove98 on the spool will establish-communication between ports 84 and 85,the time-delay mechanism may be rendered operative. The degree ofoutward movement of the stop screw will determine the length of thetime- 'delay period.

restricted orifice I83 disposed in such line. Due to the orifice I83fluid flow to the power cylinder 26, when shuttle valve48 is in elevatedposition,

will be restricted. Fluid will, therefore, be caused to fiow throughlines 88 and 93 to the end of bore 82; this fluid will move spool 88 inopposition to spring 81 until the inner end of stopscrew I88 is engagedby the inner 'end of the socket in the spool. Immediately after spool 88starts to move in opposition to spring 91 groove 98 will establish ports84 and 85 and some of the fluid from the source of pressurewill bedirected through line 81 to groove 32 and the under side of the shuttlevalve. As long as piston pressure differential will exist on oppositesides of the orifice I 83, -the higher pressure of this pressuredifferential being applied through lines 85 and 93, asabove*described,-to the end of the'spool opposite the spring 91. .Thelower pressure applied to the opposite end of 'thespool throughline I04which isconnected' with, the uppe'rjendof t power cylinder 26. 'While'this'pressure' differential exists, spool 88, willbeheld against theaction of spring .91. After the pistcnand ram cease to move the pressuredifferential'is dissipated causing equal pressures at opposite endsofthe spool '88, thus permitting spring 91 to move spool 88 toward aclosed position. Fluid pressure beneath the shuttle valve 48 will bemaintained through lines 85 and 81 until spool 88 returns to a positionto, interrupt communication between ports B and 85; This movement ofspool 88 is retarded by the restricting means .95. which opposes fluidflow from the end of the bore'82, this fluid flow being caused bymovement of piston 88 under the influence of spring 91.

, Whenspool 88 interrupts fluid flow from line 86 to line 8?, pressurebeneath shuttle valve 48 will be dissipated and spring 5| will .returnthe shuttle valve to its lowered position wherein fluid pressure .fromthe source will be .directedinto the lower end of the power cylinder;the return stroke er the piston and ram will then be effected.

It is importantto note that in the operation of the power unit theshuttle valveAB is retained in an elevated position or a position tocause movement of the piston in aworking stroke, by the fluid beingdischarged from the power unit. In order to effect such a discharge, itis, necessary that a flow of fluid'fromthe pressure source to the powerunit be maintained] While such flow is taking place,.the pressuredifferential employed to cook or set the time-delay spool for operationserves also to hold the spool ready for action. The stopping of thepiston 28 .in any manner permits the instantaneous dissipation of thepressure differential which starts the operation of the time-delay. Onefeature of the mechanism shown and described is that the shuttle spooland the time-delay spool are held against movement by spring forceindirectly by the movement of the same element, namely the piston 28.The initiation of the period of the delay is thus dependent upon theoperation of the element to which the delaying action is applied. Itwill be observed that in varying the length of the time-delay caused bythis mechanism the distance travelled by spool 88 is varied permittingmore or less fluid to be directed into the end of bore 82 for dischargethrough the restricting means 96. In all positions of adjustment of thetime-delay mechanism the diameter of the orifices in the restrictingmeans 95 remains the same.

Figs. 1 to 4, inclusive, disclose the actual construction of one form ofthe time-delay mecha- -nism. It will beobserved from Figs. 3 and 4 thatthe-check valve 9:! and flow-restricting means 96 are embodied in onepiece of the valve, these elements being carried by and movablerwith thespool '88. This spool has a transversely extending passage 105, see Fig.3, which communicates with -a longitudinally extending passage I06; thispassage terminates in a socket lill formed in the spool 88. The socketreceives a substantially cylindrical check valve body 108 which is urgedby a spring J09 toward the inner end of the socket ill-1. Body 198 hasa-resilient gasket I 10 provided on its inner end for engagement 'withthe inner end of the socket 101. T-hi-sgasket and the manner of mountingspool 1-08 for movement permits relatively unrestricted .fluid flowirombore H16, around gasket 4 H1 and into socket 101; but :preyen-ts thereverse new of ;.fiuid -'over this path.

When spring moves spool 88 toward a closed position fluid must flow rromthe end otthe bore 82 through the flow restricting means 96 which iscontained within the check valve body 108. This flow restricting meanscomprises a series of spaced wafers or disks i H in which orifices I12are provided. A series of waters is employed to permit the use of largerorifices while the effect of a small ,or minute orifice is secured. Thewafers are formed of thin material to reduce the deleterious effects ofchanges in the viscosity of the 011 due to temperature variations. 1

The disks ill are clamped between spacers H3 which comprise ring-likemembers positioned be' tween adjacent disks. This arrangement provides aseries of chambers separated by the disks H1 and communicating -onlythrough the orifices therein. Due to the alternate restrictions andchambers the fluid will be repeatedly accelerated and declera'ted sothat the force of the fluid will be continuously lessened until theeffect of a minute orifice is secured.

It has been determined that by forming an orifice through which fluid isto flow, in a thin piece of material, the effect of the orifice on theflow will be afiected less by changes in viscosity due to temperaturevariations than if the orifice is formed in thick material.

By using relativelylarge orifices the disks may be formed of heaviermaterial while the most desirable ratio of orifice diameter to lengthismaintained. Li a single minute orifice were employed and an attempt weremade to retain the same diameter to length ratio, the material would beso thin that a failure thereof would immediately result.

I claim:

1. A time delay valve comprising a body provided with a chamber, anintermediate port extending from said chamber and a laterally extendingport on either side of said intermediate port; a spool element disposedfor movement in said chamber and normally obstructing communic-ationbetween said ports; a passage formed in said spool to establishcommunication between one of said laterally extending ports and one-endof said chamber; spring means normally urging said spool element towardsaid one end .of said chamber; a check valve having an orifice disposedin the passage in said spool, said check valve serving to permitrelatively unrestricted fluid flow fromsaid port to said chamber end andcontrolled fluid flow in the opposite direction, said spool be ingmovable in response to a higher pressure in said one end of said chamberthan in the other end to a position in which communication be tween saidintermediate port and the port communicating with said one end of saidchamber is established; and means for regulating the discanoe-said spoolis moved bysuch pressure.

2. A time delay valve comprising a body provided with a chamber andfirst and second laterally extending ports spaced longitudinally .ofsaid chamber and communicating therewith, all of said ports being spacedfrom the front .end -.of said chamber; a spool member disposed forsliding movement in said chamber; resilient means yieldably urging saidspool member toward :the front end of the chamber, said spool preventingcommunication between the first and second lateral ports when in suchposition; apair of passages in said spool member for establishingcommunication between the first lateral port when :fluid pressure issupplied thereto and the front en of said chamber at the end of saidspool; a check 9 valve in one of said passages, said check valvepermitting fluid flow from the first lateral port to the front end ofsaid chamber and preventing flow in the opposite direction; and a seriesof small orifices in the other of said passages to retard fluid flowtherethrough.

3. A time delay valve comprising a body provided with a chamber andfirst and second laterally extending ports spaced longitudinally of saidchamber and communicating therewith, said ports being spaced from thefront end of said chamber; a spool member having an external groovedisposed for sliding movement in said chamber; resilient means yieldablyurging said spool member toward the front end of the chamber, said spoolpreventing communication between said first and second lateral portswhen in such position; a pair of passages for establishing communicationbetween the groove in said spool, when fluid pressure is supplied tosaid first lateral port, and the front end of said chamber at the end ofsaid spool; a check valve in one of said passages, said checl: valvepermitting fluid flow Y from said groove to the front end of saidchamber and preventing reverse flow; and a series of spaced orifices inthe other passage to retard fluid flow therethrough.

4. A time delay valve comprising a body having a chamber and first andsecond laterally extending ports communicating therewith, said portsbeing spaced from the front end of said chamber and longitudinally ofsaid body; a spool member having an external groove disposedin saidchamber for sliding movement; spring means in said body urging saidspool toward the front end of said chamber, said spool preventingcommunication between said first and second ports when disposed in suchposition, the groove in said spool establishing communication betweensuch ports when moved in opposition to said spring; a pair of passagesfor establishing communication between the groove in said spool and theforward end of the chamber beyond the corresponding end of said spool; acheck valve in one of said passages to permit fluid flow to the forwardend of said chamber and prevent flow from such end through the passage;and a restriction in the other passage to provide limited flowtherethrough.

5. A time delay valve comprising a, body having a chamber and first andsecond laterally extending ports communicating therewith, said portsbeing spaced from the front end of said chamber and longitudinally ofsaid body; a spool member having an external groove disposed in saidchamber for sliding movement; spring mean in said body urging said spooltoward the front end of said chamber, said spool preventingcommunication between said first and second ports when disposed in suchposition, the groove in said spool establishing communication betweensuch ports when moved in opposition to said spring; a pair of passagesfor establishing communication between the groove in said spool and theforward end of the chamber beyond the corresponding end of said spool; acheck valve in one of said passages to permit fluid flow to the forwardend of said chamber and prevent flow from such end through the passage;and a plurality of thin wall members dividing a portion of the otherpassage into a series of chambers, said wall members having reducedorifices to establish limited communication between said chambers.

6. A time delay valve comprising a body having a chamber and first andsecond laterally extending ports communicating therewith, said portsbeing spaced from the front end of said chamber and longitudinally ofsaid body; a spool member having an external groove disposed in saidchamber for sliding movement, spring means in said body urging saidspool toward the front end of said chamber, said spool preventingcommunication between said first and second ports when disposed in suchposition, the groove in said spool establishing communication betweensuch ports when moved in opposition to said spring; an adjustable stopmember in said body for limiting the extent of movement of said spool inopposition to said spring; a pair of passages for establishingcommunication between the groove in said spool and the forward end ofthe chamber beyond the corresponding end of said spool; a check valve inone of said passages to provide fluid flow through such passage to theforward end of said chamber and prevent fiow in the opposite direction;and a restriction in the other passage to provide limited flowtherethrough.

, CECIL E. ADAMS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 270,573 Blake Jan. 16, 1883 419,447 Hussey Jan. 14, 1890441,995 Wheeler Dec. 2, 1890 559,881 Ahrens May 12, 1896 1,379,092Fraccascia May 24, 1921 2,004,904 ,Peo June 11, 1935 2,411,930 MathysDec. 3, 1946 2,416,722 Waldie Mar. 4, 1947

